This article discusses the contribution of leading post-World War II realist scholars of international relations, notably Hans Morgenthau, George Kennan, and Arnold Wolfers. I first critique the still widespread misconception that post-WWII realist scholarship does not fundamentally differ in its ethical outlook from either Hobbesian moral skepticism or Machiavellian thinking in the reasons of state tradition. Thereafter, I elucidate the moral foundations of twentieth-century realism and point out some of its inherent inconsistencies and tensions. In the second part of the article, I discuss the realists’ consequentialist critique of American policies aimed at promoting liberalism and democracy by force, as well as their warnings against unrestrained U.S. unilateralism, and I assess the relevance of their arguments to contemporary international relations.